Suspected vagal reflex and hyperkalaemia inducing asystole in an anaesthetised horse

Abstract

Vagal reflexes have been well documented in both human and veterinary anaesthetic literature. A trigeminocardiac reflex (TCR) is a vagal reflex frequently documented in human medicine, and subtypes such as the oculocardiac reflex (OCR) are well documented in veterinary medicine throughout numerous species. 1-3 A further TCR subtype, the maxillomandibulocardiac reflex (MCR) has been documented in human literature associated with facial fractures and has recently been described in a sole case report in a dog. 4 Thus far, it has not been documented in a horse. The current case report aims to describe the perianaesthetic management of a horse that developed asystole due to a suspected TCR of either OCR or MCR in origin, in combination with hyperkalaemia of unknown cause which may or may not have contributed to the suspected vagal event, a relationship that has been previously documented. 5,6 Both causes will be discussed as independent or contributory factors.

Hyperkalaemia in a greyhound under general anaesthesia

“…These reports have known aetiologies of malignant hyperthermia 22 and hyperkalaemic period paralysis, 23 with one case report of hyperkalaemia in an anaesthetised horse having an unknown cause. 24 Acute perianaesthetic hyperkalaemia is less frequently reported in human medicine; however, suspected aetiologies relate to drug administration, decreased renal excretion and increased cellular potassium release. 25 There have been historical case reports of hyperkalaemia associated with 'propofol infusion syndrome' during long-term sedation of human patients with propofol.…”

“…Hyperkalaemia has also been reported in horses under general anaesthesia. These reports have known aetiologies of malignant hyperthermia 22 and hyperkalaemic period paralysis, 23 with one case report of hyperkalaemia in an anaesthetised horse having an unknown cause 24 …”

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“…69 Case reports can be used to introduce new technology which is likely to be of interest to other clinicians, 70 and they are particularly appropriate for communicating adverse events where the authors are seeking to share the benefit of their experience in the hope that it will be helpful to others unfortunate enough to encounter the same challenge. Excellent examples of this use of case reports are accounts of successful solutions for complications during equine anaesthesia 71,72 and a description of the management of a horse which was accidentally given formalin via nasogastric tube due to misidentification of the contents of storage containers. In the latter case report, intensive management of the affected horse ultimately led to successful discharge from the hospital.…”